BARS (or "split sphere") is a high-pressure high-temperature apparatus usually used for growing or processing minerals, especially diamond. The name is a transliteration of a Russian abbreviation БАРС = Беспрессовая Аппаратура высокого давления "Разрезная Сфера" (press-free high-pressure setup "split sphere"). Typical pressures and temperatures achievable with BARS are 10 GPa and 2500°C.
The BARS technology was invented around 1989–1991 by the scientists from the Institute of Geology and Geophysics of the Siberian branch of the Academy of Sciences of the USSR. In the center of the device, there is a ceramic cylindrical reaction cell of about 2 cm3 in size. The cell is placed into a cubic-shaped pressure-transmitting material, which is pressed by elements made from cemented carbide (VK10 hard alloy). The outer octahedral cavity is pressed by 8 steel sectors. After mounting, the whole assembly is locked in a disc-type barrel with a diameter ~1 meter. The barrel is filled with oil, which pressurizes upon heating; the oil pressure is transferred to the central cell. The central cell is heated up by a coaxial graphite heater. Temperature is measured with a thermocouple.
The growth rate for 5 carats (1.0 g) type Ib (yellow, nitrogen-rich) crystals using Fe–Ni catalyst reaches as high as ~20 mg/h towards the end of 100 h growth cycle, i.e. crystals of 5 carats (1.0 g) to 6 carats (1.2 g) can be grown in less than 100 h.
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